1. Field of the Invention
This application relates to a turbine in fluid, particularly to a turbine with the axis of rotation lying in a plane transverse to the direction of flow of the fluid.
2. Description of Related Art
A number of transverse axis wind turbines, such as U.S. Pat. Nos. 4,113,408, 4,186,313, 4,822,239, 5,195,871, 6,853,096 and 6,619,921 German Patent Application Publication Number DE 10 2005 011 501 A1, Chinese Patent Application Publication Number CN 101021203A, PCT International Application Publication Number WO 2006/041464, and European Patent Application Publication No. 1541866 have been proposed with various controlled rotatable blades according to the direction of flows.
As it is shown, there have been standing needs for a fluid turbine that would provide any improvement from the existing fluid turbines and that meets one or more of the requirements shown above.
Long in human history, the dynamic energy in flowing fluid has been used to help irrigation and carry out farm works. Water wheels and windmills were built to capture energy in flowing water and wind. As more and more sophisticated techniques were developed, many types of machines were constructed and these machines were generally named as turbines.
In general, turbines with the axis of rotation parallel to the direction of flow are called axial flow turbines and those with the axis of rotation lying in a transverse plane (a plane that is perpendicular to the direction of flow) are called transverse axis turbines. Turbines are also described as horizontal axis or vertical axis turbines depending respectively on the orientation of the axis of rotation of the turbine.
Turbines may also be classified according to the working principle that they employ to extract energy from the flowing fluid. If the rotation is energized by lift force, the turbine is said to be of the lift type. Similarly, if drag force is used, the turbine is of the drag type. There are also hybrid turbines which make use of both lift and drag forces.
For a fluid turbine to be practical, at least several of the following requirements have to be fulfilled:
1. Low equipment fabrication cost;
2. Low equipment transportation cost to site;
3. Low site construction and erection costs;
4. Low maintenance cost;
5. High energy capturing to total cost ratio;
6. Energy capturing power of the turbine or turbine system can be designed to suit local topographic and environmental conditions;
7. Ability to operate in both laminar and turbulent fluid flow;
8. Ability to self start at low fluid speed;
9. Ability to handle high fluid speed without causing damage to the system;
10. Ability to operate continuously year round in all weather conditions;
11. High energy capture ratio with respect to the foot print of the turbine;
12. High energy capture ratio with respect to the exposed frontal projected area of the turbine facing the flowing fluid;
13. High exposed area to the flowing fluid with respect to the foot print of the turbine;
14. Low noise level during operation; and/or
15. Low environmental impact including change of ecology and hazard to living things.